1. Field of the Invention
The instant invention is a method for the control of undesirable plants by use of plant pathogens.
2. Description of the Prior Art
The merits for using plant pathogens to control weeds in annual crops have been discussed previously for two Colletotrichum spp. (Daniel, et al. U.S. Pat. No. 3,849,104 and Templeton, U.S. Pat. No. 3,999,973). The anthracnose fungus Colletotrichum gloeosporioides has been used to control the weed northern jointvetch, and another strain of this fungus has been used to control winged waterprimrose. Colletotrichum malvarum has been used to control prickly sida. These three pathogens have been combined to control all three target weeds at once. In other work the fungus Alternaria cassiae (U.S. Pat. No. 4,390,360) has been used to control sicklepod, coffee senna, and showy crotalaria. Another fungus Fusarium lateritium (U.S. Pat. No. 4,419,120) has been used to control prickly sida, velvetleaf and spurred anoda. Included in this same patent, the synergistic interaction between F. lateritium and Alternaria macrospora has been used for control of spurred anoda.
Cercospora rodmanii has been used to control waterhyacinth (U.S. Pat. No. 4,097,261) and Phytophthora palmavora has been commercially developed as a biological herbicide for stranglervine.
Wild poinsettia (Euphorbia heterophylla L.) is a major weed problem in portions of the southern United States, Brazil, Columbia, Peru, Nigeria, and in several other countries which have tropical or subtropical climates (Akobundu, I.O. [1982] Weed Science 30: 331-334; Bannon, J. S., Baker, J. B. and Rogers, R. L. [1978] Weed Science 26: 221-225; Reed, C. F. [1977] U.S. Dept. Agric. Handbook No. 498). This annual species reduces yield through direct competition with crop plants and interferes with harvesting. The plants produce a sticky latex sap that interferes with harvesting and reduces seed quality of soybeans by increasing moisture levels and trash accumulation (Harger, T. R. and Nester, P. R. [1980] Louisiana Agric. 23(3): 4-5; Langston, V. B. and Harger, T. R. [1983] Proc. South. Weed Sci. Soc. 36: 77).
Wild poinsettia or "painted leaf" is an annual herb that commonly has two leaf shapes; long, narrow leaves, and wider, lobed leaves. Both leaf shapes can occur on the same plants. As plants mature, the foliage develops numerous dark spots (Bannon et al., supra).
Seed germination is greatly influenced by light and temperature. Seeds remain viable in soil for extended periods of time, and maximum germination rates occur as the soil temperatures increase in late spring and early summer (Bannon et al. and Harger et al., supra).
Wild poinsettia is difficult and expensive to control using conventional weed control practices. Planting soybeans early in the growing season before wild poinsettia seedlings emerge has been shown to provide some control. Chemical herbicides recommended for control of wild poinsettia include metribuzin, linuron, acifluorfen, and dinoseb. Multiple herbicide applications are often necessary for satisfactory control (Harger et al., supra).
Spotted spurge (Euphoriba maculata L.) is an annual species that is native to the eastern two-thirds of the United States. The leaves are oblong or lance-falcate, 0.8-3.5 cm long, with edges that are slightly toothed. A conspicuous reddish spot usually occurs at the base of each leaf. Spotted spurge is a major weed problem in soybeans, cotton, and other agronomic crops. Crop yields are reduced through direct competition. In addition, the milky sap present in the stems causes difficulty in harvesting.
Effective chemical control of spotted spurge is both difficult and expensive. Norflurazon is used in cotton, and in soybeans the herbicides used include acifluorfen, metribuzin, and dinoseb.
There is a need to have an effective means for the biological control of wild poinsettia and weedy spurges, for example, spotted spurge. Such a means would, advantageously, eliminate, or at least reduce the use of chemical agents to control these weeds. It is well known that the extensive use of chemicals to control weeds over the last twenty years has placed a heavy burden on the ecosystem, resulting in contamination of groundwater, lakes, rivers, etc. The substitution of biological control agents for many of these chemicals is recognized as a solution to this chemical contamination problem.